The invention relates to a method for the protected transmission of data with a telecopying system incorporating a sending device, a receiving device and a transmission link inbetween, as well as one device each at the transmitting and the receiving ends for the execution of the method.
It must be understood that in connection with the definition of the invention and the execution of the method according to the invention, no differences between the terms "device", "appliance", "apparatus" and other words of similar meaning are to be insinuated. The different parts of the system required for the execution of the method, which in relation to the transmitting link are located at the transmitting end or at the receiving end, can be separate, or partly or fully integrated.
Besides, it must be understood that in connection with the definition of the invention and the execution of the method according to the invention:
The qualification of a feature as "visible" signifies that the presence of this feature can be detected with the naked eye. However, it does not mean that the visible item can be clearly identified as sign, symbol, code or the like, and even less that the visible item clearly carries a piece of information that can be utilized by humans. For example, spots distributed at random on a document are "visible", but one cannot recognize in them any kind of writing and no sense whatsoever.
The qualification of a feature as "legible" signifies that the presence of this feature can be ascertained with the naked eye and that the visible item can be clearly identified as sign, symbol, code or the like. However, it does not mean that the visible item clearly carries a piece of information that can be utilized by humans. For example, characters of an unknown language put together in a certain order on a document are "legible", yet no sense is recognized in them, i.e. no information.
The qualification of a feature as "intelligible" signifies that (i) the presence of this feature can be ascertained with the naked eye and that (ii) the visible item can be clearly identified as sign, symbol, code or the like, and that (iii) it clearly carries a piece of information that can be utilized by humans. For instance, texts written on a document in a known set of characters and language are "intelligible".
Graphic representations can be visible, legible or intelligible, depending on their shape.
Encoding (ciphering) renders intelligible data non-intelligible but leaves them legible. Decoding (deciphering) renders non-intelligible but legible data intelligible.
Since encoded data is non-intelligible, its transmission in a telecopying system requires measures to be taken in order to guarantee its legibility, because illegible parts of data cannot be decoded anymore, which means that a part of the message to be transmitted has been finally lost.
The most obvious measure for the transmission of encoded data, while guaranteeing the decoding possibility, is error-free data transmission.
Error-free data transmission through a transmission link which is not distortion-free can in general be accomplished by means of transmission protocols and/or by the transfer of additional information: these measures permit a regeneration of the distorted information. The required additional information may be, for example, that the information is encoded in characters which can be recognized by a reading device in spite of a certain distortion (for example, the OCR-fonts were devised for this purpose). Yet, the transmission link must still meet certain minimum requirements as regards transmission safety; only if these minimum requirements have been met is it possible to transmit encoded and thus non-intelligible data.
These minimum requirements, however, will not have been met, if the transmission link is susceptible to errors and/or involves an optical interface having a high distortion factor. In this case, the transmission errors become so frequent and/or of such a kind that no error correction is possible, thus rendering the transmission of encoded and thus non-intelligible data impossible.
The nowadays customary telecopying system that scans a document line by line, and creates a copy of it, line by line, is an example of a transmission link with an optical interface, which possesses a high distortion factor. It is a known fact that the reproduction of the original on the telecopy of a telecopying system often contains already errors in the direction of the lines (full lines may be missing), even though in a yet tolerable measure. Nevertheless, at a right angle to the direction of the lines (i.e. in the direction of paper transport), there are often large distortions which may be so large that parts of the text may be missing or so illegible that somebody cannot even guess the meaning of a plain text by means of the copy and needs to request the repetition of the transmission.
Telecopying systems are already being developed that are not required to scan a document explicitly line by line and produce a copy of it line by line. For example, the document may be scanned by means of a matrix of CCD-sensors, thus resulting in extreme cases in an completely parallel and not in a serial scanning. Nevertheless, the signals supplied by the matrix must be transferred entirely serially (bit by bit) on a one-channel transmission link. While on a multi-channel transmission link the transmission is done in a parallel way (all bits of e.g. a byte or word in parallel), the transmission of the bytes or words is still serial. Thus, such telecopying systems are still operating in a serial mode, even though this is only implicit.
The same problems connected with serial transmission remain to be solved, regardless of whether the telecopying system operates explicitly or implicitly in a serial mode.
If the information transmitted is encoded data that is non-intelligible, there exists no possibility of correcting errors by means of the human intellect or of regenerating missing data. This can be deduced from the fact that encoded data possesses the character of random data. In such circumstances the transmission of encoded and thus non-intelligible data is impossible.
Yet, there is a demand for the transmission of encoded and thus non-intelligible data by way of a customary telecopying system. For example, business people on trips want to be able to take advantage of the telecopying facilities that are nowadays provided in modern hotels and press centers of exhibitions, fairs, etc. and that are accessible to the public, in order to transmit messages rapidly and with ease. On the other hand, and especially in these circumstances, there exists the great danger that also one's rivals learn about this exchange of information by telecopying machine in an unduly way, for example, by accidentally or on purpose reading the messages, for instance on the telecopier in the press center, or even by tapping of the transmission link.
Hence, it had been long-cherished, however, not possible so far to transmit a confidential piece of information by means of an entirely customary, publicly accessible telecopying system in a legible but non-intelligible way. The frequently deficient and heavily scattering quality of the data transmission of a telecopying system has so far not allowed to convert a plain text or a graphics into encoded data, to write it, for example, in OCR-font or in any given symbols on paper, to have the resulting document transmitted via a customary, publicly accessible telecopying system, to receive the transmitted copy of the document by means of a reading or recognition device (for example with a scanner with a recognition program for OCR-font or symbols), to decode the signals from the reading or recognition device in a deciphering device, and to print the decoded data or display it on the monitor: the transmission via a customary telecopying system is not good enough so as to guarantee at the receiving end that all OCR-characters or symbols will be recognized without errors, while an insecurity cannot be remedied by means of reasoning, as is the case with plain text, because the data are encoded. In the most unfortunate of cases, a read error may occur at the beginning of the transmitted message and render impossible the decoding of the entire piece of information.
Most recent developments in the field of telecopying systems give rise to expectations that before long telecopying systems will be available which are able to process also OCR-font with adequate transmission quality and optical resolution, thus guaranteeing at the receiving end that all OCR-characters will be recognized without error. Yet, the great existing amount of customary telecopying systems installed is not going to be replaced immediately and everywhere by telecopying systems of this new generation, not least for financial reasons. The previously mentioned disadvantages of the customary telecopying systems will therefore continue yet for quite some time and need to be overcome.
Therefore, it is the object of the invention to permit protected data transmission of non-intelligible data by using customary telecopying systems.
It is known to input the "original" data to be transmitted into a ciphering and output device that encodes it and outputs the resulting encoded data on a paper tape. The paper tape carries legible data as holes punched into the paper, however, which in their encoded form is non-intelligible for non-authorized persons. The paper tape is now fed into a sending device that scans the legible data on the paper tape line by line in combination with the line feed. The result of the scan is transmitted by the sending device as converted electric signals through a transmission link to a receiving device. The receiving device produces a copy of the punched paper tape according to the received signals, on which the data is legible but in its encoded form non-intelligible for non-authorized persons. This copy is fed into a reading and deciphering device which reads the data off the paper tape, deciphers it, and outputs the resulting deciphered data to an outputting device that restores the original data and makes it available for further processing as intelligible data on paper or at the monitor (for example by visualization, for machine control, etc.).
This known type of protected data transmission functions only in combination with a paper tape punch and a paper tape reader, which are compatible with the usual public telex system but not compatible with the usual public telecopying system. However, it is known that the public telex traffic is decreasing these days, while the public telecopying traffic is increasing strongly: hence, a solution based on punched paper tape and telex traffic does not correspond to the current circumstances and to user needs. The telecopying of a punched paper tape is not a reasonable alternative.
From DE-A-3230201 a system for the protected transmission of data is known that is equipped with a telecopying system comprising a sending device, a receiving device, and a transmission link in between. In this system the telecopying system is not a fully customary, publicly accessible telecopying system. The ciphering device is integrated with the sending device and the deciphering device with the receiving device. This system does not solve the previously stated object of the invention.
From U.S. Pat. No. 4,339,820 and GB-A-2101376 methods and devices for the ciphering and deciphering of intelligible data are known: The ciphered data is legible on a document as bar code. These methods and devices are in no way connected to any telecopying system and the art disclosed in U.S. Pat. No. 4,339,820 and GB-A-2101376 deals by no means with the solving of transmission problems. These methods and devices cannot contribute anything to the solution of the previously mentioned object of the invention.